1. Field of the Invention
This invention relates to electrochemical gas sensors and more particularly to a non-aqueous electrolyte for use in a three electrode chemical cell.
2. Description of the Prior Art
U.S. Pat. No. 3,776,832 to Oswin et al. which issued on Dec. 4, 1973 describes a three electrode electrochemical gas sensor which can be adapted to measure oxidizable or reducible gases, such as chlorine, CO, Cl.sub.2 and hydrazine, as well as other gases. This particular known cell has two shortcomings. Firstly, it requires an aqueous electrolyte which has a limited service life due to evaporation of the electrolyte. Secondly, the temperature range within which the cell can operate is limited due to the possibility of freezing of the electrolyte.
The shortcomings noted above as a result of using an aqueous electrolyte have been recognized for some time. U.S. Pat. No. 4,184,937, which issued on Jan. 22, 1980 to H. Tataria et al. entitled "Electrochemical Cell for the Detection of Chlorine", describes a three electrode cell with a non-aqueous electrolyte consisting preferably of lithium perchlorate dissolved in an organic solvent selected from the group consisting of gamma-butyrolactone and propylene carbonate. The non-aqueous electrolyte has a considerably lower freezing point and vapor pressure than an aqueous electrolyte. The electrodes for use in the two or three electrode electrochemical cells are comprised of either gold or platinum black.
In U.S. Pat. No. 4,201,634, which issued on May 6, 1980 to J. R. Stetter entitled "Method for the Detection of Hydrazine", a three electrode electrochemical cell is described using an aqueous alkaline electrolyte (KOH) in contact with the sensing electrode. The sensing electrode comprises a noble metal catalyst bonded to a hydrophobic material to provide a diffusion electrode. The catalyst is described as rhodium or gold and the hydrophobic material is described as polytetrafluoroethylene.
In a publication by J. A. Plambeck, published in Electro Analytical Chemistry, Wiley-Interscience, pages 50-51, New York, N.Y. (1982), a potentiostat is described for maintaining a sensing electrode of an electrochemical cell at a fixed potential with respect to its reference electrode.
It is therefore desirable to provide an electrochemical gas sensor particularly suited for detecting hydrazine in a three electrode electrochemical cell where the electrolyte is n-methyl-2-pyrrolidone having tetraalkyl ammonium salt therein.